1. Field of the Invention
The invention relates to devices for use in imaging organs and tissues of a body. More specifically, the invention relates to an apparatus for securing such an imaging device to a body so the imaging device will remain in a fixed position relative to the body yet the body will be able to move freely during the imaging process.
2. History of the Prior Art
Imaging devices are routinely used in medicine to obtain images of body organs and tissues. Such devices include conventional "X-ray" devices, positron emission tomography (PET) detectors, single positron emission computed tomography (SPECT) detectors, fast computed tomography (cine-CT) detectors, gamma cameras, and the like. Although used in different contexts and with different organs, all imaging devices presently used in medical applications share the requirement that the body to be imaged remain as stationary as possible with respect to the device so an accurate image may be obtained.
However, it is not possible to completely immobilize the human chest and abdomen for imaging of organs such as the heart due to involuntary movement (e.g., heartbeat). To compensate for such movement, several images may be obtained from which a composite image of the organ may be extrapolated. For example, cine-CT scanners typically obtain multiple images of organs in a matter of seconds. Through mathematical calculations and image manipulation, the series of images is combined into a single image. However, the utility of the image is limited by loss of information during the image combination step and dissipation of contrast agent from spaces within the organ (e.g., cardiac ventricles).
The problem of movement is particularly acute when evaluating heart function under stress. For example, radioisotopic imaging of the heart is a routine diagnostic procedure used to evaluate patients for coronary artery disease (CAD). In patients with CAD, ventricular function and myocardial perfusion (arterial blood flow) rates may be within normal ranges at rest, but become abnormal during physical stress. For that reason, CAD is commonly evaluated immediately after the patient has exercised (e.g., the treadmill stress test) or after the patient has received drugs to simulate the effects of exercise.
However, because the heart cannot be adequately imaged while the patient is in motion, patients may be instructed to stop moving before the images are taken. Under this approach, no information is obtained directly from the heart at peak stress or while stress on the heart develops. In an effort to obtain such information, patients may be instructed to grip or press their chest against the imaging device while exercising.
The difficulties inherent in attempting to stabilize a moving body against a stationary imaging device are apparent. Not only is the patient's freedom of movement compromised, but it is not uncommon for the patient to collide with the device during motion, thus potentially compromising the latter's accuracy. Yet the alternative of moving the imaging device with the patient's body is made difficult, if not impossible, by the weight and size of such devices. Indeed, conventional Anger gamma cameras (so named after their inventor) are typically so heavy that they must be attached to a motorized gantry to allow the camera to be moved into position for imaging.
In an effort to obtain information for use in evaluating ventricular function during stress on the heart, several researchers have attempted to use radioisotopic probes to assess heart function without imaging. For example, one approach strapped such a probe directly onto the patient's chest, presumably over the position of the left ventricle. However, without images to use for confirmation, it proved difficult to be certain that the probe was properly positioned. Moreover, although such a probe could (if properly positioned) assess ventricular function in terms of ejection fraction (EF), it cannot be used to assess regional movement of the ventricular wall. Therefore, although easily moved and attached to a body, radioisotopic probes have proven to have limited usefulness.
Thus, a need exists for an apparatus which will allow medical quality images to be obtained of body organs while the body is in movement or otherwise under stress. The present invention addresses that need.